Billet holder for cutting and slicing apparatus

ABSTRACT

A holder is provided for a billet of material, such as a silicon or germanium crystal encapsulated in a plastic material, that is to be cut into thin, wafer-like slices. The billet is maintained in the holder by three point contact at both its upper and lower extremities and throughout its full movement from the first wafer to be cut or sliced to the last wafer that can be cut from the billet. In addition to the improved holding of the billet, the encapsulated crystal can be mounted so that a positive and constant holding force is exerted thereagainst, so that no cantilever effect can result during the cutting operation, thereby generally eliminating any lateral movement of the billet relative to the cutting element upon contact therewith.

Lane

1 Apr. 9, 1974 SLICING APPARATUS BILLET HOLDER FOR CUTTING AND [75] Inventor: Richard L. Lane, Penfield, NY.

[73] Assignee: Kayex Corporation, Rochester, NY.

[22] Filed: June 8, 1972 [21] Appl.No.: 261,091

[52] US. Cl. 125/13 R, 51/73 R, 51/215 H [51] Int. Cl B2811 1/04 [581 Field of Search..... 51/73 R, 215 1-1; 125/15, 125/13 [56] References Cited UNITED STATES PATENTS 3,662,733 5/1972 Okamoto 51/73 R Primary Examinerllarold D. Whitehead Attorney, Agent, or Firm-Lloyd F. Seebach [57] ABSTRACT A holder is provided for a billet of material, such as a silicon or germanium crystal encapsulated in a plastic material, that is to be cut into thin, wafer-like slices. The billet is maintained in the holder by three point contact at both its upper and lower extremities and throughout its full movement from the first wafer to be cut or sliced to the last wafer that can be cut from the billet. In addition to the improved holding of the billet, the encapsulated crystal can be mounted so that a positive and constant holding force is exerted thereagainst, so that no cantilever effect can result during the cutting operation, thereby generally eliminating any lateral movement of the billet relative to the cutting element upon contact therewith.

5 Claims, 5 Drawing Figures PATENTEDAFR 91974 $802,412

sum 2 [IF 2 FIG 4 BILLET HOLDER FOR CUTTING AND SLICING APPARATUS FIELD OF THE INVENTION This invention relates to cutting and slicing apparatus and, more particularly, to a device for holding the material or billet, such a silicon or germanium crystal, that is to be cut into thin, wafer-like slices with a positive and constant force as it is moved relative to the cutting 1 element.

DESCRIPTION OF THE PRIOR ART Crystals of very small size are used in the manufacture of transistors and rectifiers. These crystals comprise, thin wafer-like sheets or slices which, after lapping to a desired thickness and having been polished to obtain a smooth surface finish, are ultimately cut into small pieces to form transistors or rectifiers. Crystals of the type referred to above are very hard and very brittle. Each slice of a crystal is out much thicker than actually required and is then lapped to reduce the slice to the required thickness. This proceedure has been necessary because, apparatus had not previously been available which could slice such crystals and, at the same time, produce the smoothness of surface and the required degree of parallelism of the surfaces that is required. In addition, the method by which such wafers are cut necessitates that the billet be held and maintained in a very accurate relationship to the cutting element.

The ability to handle a crystal of considerable length is accomplished by mounting the crystal above a horizontal, annular cutting member and allowing the severed slices to fall away from the cutting member and into a receptacle. Since the crystals can be of irregular cross section and can be relatively small in diameter, a single large diameteror a number of small diameter crystals with their longitudinal axes parallel can be conveniently handled by encapsulating the crystal or crys talsin a plastic material.

Such an encapsulated crystal is mounted as a billet to a wooden or metal block known as a billetmounting or guide block. This block is normally held under spring tension in a billet holder which is mounted on the 'cutting and slicing apparatus. As the slices are cut from the billet, the billet and attached guide block are moved or extruded from the billet holderby an indexing device, such as a lead screw. Normally, the resistance of the billet to lateral motion of the lower end is very poor. This lateral motion of the billet during slicing causes broken wafers, tapered wafers, or wafers having a poor degree of flatness. The spring tension on the guide block is the only force holding the billet. Support of the lower end, where cutting is taking place, is primarily by cantilever effect. With such a mounting'of the billet, it must be periodically adjusted as the wafers are being sliced and such adjustments are not always reproducable. In addition, the crystal is not always centered relative to the axis of the cutting element and additional adjustments must be made for crystals of different size. Another disadvantage that sincethe lead screw cannot always be centered on the billet, an even and smooth extruded movement cannot always be obtained.

SUMMARY OF THE INVENTION It is a primary object of the invention to provide a billet holder which will require very little, if any, manual adjustment to maintain a billet in the holder with the necessary holding force to alleviate lateral movement thereof relative to a cutting element.

It is still another object of the invention to provide a billet holder which will exert a positive and constant 0 holding force at each end of a billet regardless of its length.

It is yet another object of the invention to provide a billet holder which permits a billet of most any size positioned in the holder to be centered relative to a lead screw, as well as centered in the holder and relative to an annular cutting blade.

It is a further object of the invention to provide a billet holder which can be easily mounted on and removed from the cutting apparatus to permit mounting of the billet per se in the holder and apart from the cutting apparatus.

In the present device, the disadvantages enumerated above are overcome in that a billet holder is provided in which the billet is maintained in the holder by three point contact at both its upper and lower extremities and throughout its full movement from the first wafer to be cut or sliced to the last wafer that can be cut from the billet. In addition to the improved holding of the billet, the encapsulated crystal can be mounted so that a positive and constant holding force is exerted thereagainst, so that no cantilever effect can result during the cutting operation, thereby generally eliminating any lateral'movement of the billet relative to the cut ting element upon contact therewith.

A mounting block is provided with a first resilient means which bears against the billet holder or casing relative to one end of the crystal and the casing is provided with a second resilient means which bears against the other end of the encapsulated crystal. Due to the manner in which the encapsulated crystal is mounted, a three point contact at both extremities of the crystal is obtained so that the force with which the crystal is held in the holder is both positive and uniform. Further, the force excited at the end adjacent the cutting element is sufficient to prevent any lateral movement of the billet when it is moved relative to the cutting element to cut a slice therefrom. As the cutting of the billet into slices nears completion, the upper spring or first resilient member-overrides the lower or second resilient member, thereby permitting all of the billet to be cut with an equivalent force being still exerted thereagainst.

These and other objects and advantages of the invention will be apparent to those skilled in the art by the following description of a preferred embodiment of the invention.

DESCRIPTION OF THE DRAWINGS Reference is now made to the accompanying drawings wherein like reference numerals and characters designate like parts and wherein:

FIG. 1 is a partial vertical sectional view through a cutting and slicing apparatus showing one embodiment of a billet holder for mounting the billet relative to a cutting member and a lead screw for extruding the billet from the holder;

FIG. 2 is a plan view showing the arrangement of the crystal and its guide block within the billet holder shown in FIG. 1;

FIG. 3 is a front elevational view of a preferred embodiment of the invention with the cover of the billet holder removed from the casing and showing a billet mounted within the casing;

FIG. 4 is a plan view of the billet holder shown in FIG. 3 with the cover in a closed and assembled position; and

FIG. 5 is a vertical section taken substantially along the line 55 in FIG. 4 and showing the relationship of the resilient holding members to a billet mounted and retained within the casing of the billet holder.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With particular reference to FIG. 1, the apparatus disclosed therein is similar to that disclosed in U. S. Pat. No. 3,039,235 entitled CUTTING APPARATUS and issued to R. G. Heinrich on June 19, I962. In such apparatus, an annular sawblade generally designated by the numeral is provided with an inner, annular cutting portion 11. Such a sawblade is commonly referred to as an ID" blade, the cutting element per se comprising an abrasive grit, such as diamond dust in a carrier, which is adherred to the inner edge of a central opening in the sawblade and the immediately adjacent surfaces of the sawblade in a well-known manner. The sawblade 10 is mounted between a first ring 12 and a second ring 13 and formed with an annular deformation 14 which radially tensions the sawblade. These rings 12 and 13 are carried by a third ring 15. The blade and ring structure forms a unit removably mounted on a support member 16 that is rotatable at a relatively high speed. A receptacle 17 is arranged beneath the sawblade 10 to receive the thin slices or wafers that are cut from the billet designated by the numeral 20.

As mentioned hereinabove, the billet 20 can comprise one or more crystals encapsulated in a plastic material. However, the invention is not to be considered as being confined to only a holder for one or more crystals but can be utilized for cutting and slicing many materials where the same problem exists, i.e., holding the material against lateral movement when it is moved relative to a cutting element. Hence, the term billet" as used hereinafter is meant to include not only one or more crystals per se but any material of similar form and whether encapsulated or not.

Normally, the crystal 20, whether or not encapsulated is secured to a mount or guide block 21 by means of an epoxy or wax for the cutting and slicing operation. The billet holder 22 comprises a generally U- shaped member 23 having a rear wall 24 for mounting the holder on the apparatus and extending side walls 25 and 26, the latter being joined by a cover member 27 that is pivotally mounted on one of walls 25 or 26, so as to completely enclose and surround the crystal 21 and the guide block 21. The holder 22 is provided with a resiliently mounted plate 28 having a plurality of spring fingers 29 that engage one side of the guide block 21, as seen in FIG. 1. The force with which the spring fingers 29 engage the block 21 is determined by the adjustable screws 30 which bear against the plate 28 through the media of springs 31 which, in turn, form a resilient mount for plate 28, the block 21 being urged thereby against cover 27. The block 21 is also engaged by a second set of adjustable screws 30' and springs 31 by which block 21 is urged against wall 25. A lead screw 35 that is movable axially into engagement with block 21 is driven by means of a threaded pulley 36 associated with lead screw 35, a belt 37, and a pulley 38 on the shaft of a motor 39. The lead screw is held against rotation by a key carried by a fixed guide member 40, the key engaging an axial slot (not shown) in lead screw 35. With this arrangement, rotation of the pulley 36 through the media of motor 39 will cause the lead screw 35 to move axially and bear against guide block 21, thereby extruding the end 41 of the billet 20 from the billet holder 22 and into and relative to the central opening of the sawblade 10. The amount of extrusion will be in accordance with the thickness of the slide or wafer to be cut.

As shown and described in the above-mentioned patent, the billet holder 22, lead screw 35, motor 39 and other associated parts are movable in one direction relative to the fixed sawblade 10 and with rotation of the sawblade, a wafer is then cut from the end 41 of the crystal 21 by the cutting element 11 of the sawblade. These parts are then moved in the opposite direction to again position the billet and billet holder relative to the central opening of the sawblade. When in this position, the billet is then extruded the necessary distance for establishing the thickness of the next slice to be cut from the end 41.

It should be evident that as the crystal or billet 20 is moved against the cutting element 11, a force is exerted against the end 41 which causes the crystal to move or turn about the block 21 with a cantilever action or effect. With the end of the crystal more or less hanging free, this force is of greatest magnitude when the crystal is at its longest length. Normally, the force will decrease with each slice that is removed from the crystal or, in other words, as the length of the crystal decreases. In order to overcome the shortcomings of the embodiment disclosed in FIG. 1, an arrangement, such as that disclosed in FIGS. 3-5, produces a mounting for the crystal or billet that is much superior and presents many advantages over other holding devices, such as that shown in FIGS. 1 and 2.

With reference to FIG. 4, the billet holder 45 comprises a casing and a cover 55. The casing 50 includes a back plate 51 by which the casing is mounted on the apparatus and extending side plates 52 and 53. The side plate 52 is provided with hinge members 54 for receiving cooperating members fixed to cover 55. The cover 55 is secured in a closed position by a number of pivotally mounted thumb screws 56, see FIG. 3. The inner surface of the cover 55 carries a guide member 57 having a recess 58 which extends the length of cover 55 and can extend therefrom, as seen in FIG. 5, to provide a support or backing for billet 60 that is as close as possible to the cutting plane. The recess 58 is preferably V-shaped in cross section, see FIG. 4; how ever, other shapes can also be used which will conform to the geometry of billet 60. The purpose of the guide member 57 will be apparent from the description which follows.

With reference particularly to FIGS. 4 and 5, the encapsulated crystal or billet 60 is mounted on the end of a guide block 61 made of wood or other suitable material, preferably inexpensive enough so as to be considered expendable or disposable. At the time of such mounting, a layer 62 of epoxy or wax is cast completely along the billet and guide block 61 in a form which will conform to that of the recess 58 in guide member 57. With this arrangement, a bearing surface is provided along the guide member 57 for the full length of the crystal, as seen in FIG. 5. A U-shaped block 63 is mounted on guide block 61 and has a cross section best seen in FIG. 5. The block 63 is secured to guide block 61 by screws 64 and carries on each of the extensions thereof, designated by the numeral 65, a leaf spring 66 which bears against the inner surface 67 of plate 51.

Along the inner surface 67 of plate 51 and near the lower extremity of casing 50, a leaf spring 68 is pivotally mounted at 69 on surface 67 and has an end 70 which bears against the facing or peripheral surface of the crystal or billet 60. The force with which the end.

70 bears against the crystal or billet 60 can be adjusted by a thumb screw 71 which is carried by the plateSl. In place of screw 71, a cam can be used in conjunction with an index scale. This latter arrangement will provide means for more easily reproducing the force with which end 70 bears against billet 60. From FIG. 4 it will be noticed that leaf spring 68 is arranged between leaf springs 66; that is, as seen in the plan view. However, as block 61 and crystal or billet 60 are moved in a di rection toward the sawblade by a lead screw in much the same manner as shown and described with respect to FIG. 1, spring 68 and springs 66 hold the crystal or billet in the guide member 57.with a positive and generally uniform force. This positive force exerted particularly at the lower end of the crystal or billet prevents any cantilever effect and results in the 'cutting of a wafer having surfaces that are not only smoother but also more parallel.

As the crystal or billet is moved in a direction to extrude a portion for establishing the thickness of the slice to be cut, this positive force is maintained. As the crystal or billet is extruded and the guide block 61 reaches a position in close proximity to the sawblade, the end 70 of spring 68 will ride off of the crystal or billet 60 and engage either the guide block 61 or the U- shapcd block 63. However, the uniform force will be maintained because the springs 66 and 68 will still be holding the crystal or billet in the guide member 57. When this condition exists, any cantilever effect will be at a minimum and readily offset by the force exerted by springs 66 and 68. Hence, the crystal or billet 60 is held in guide member 57 with a force that is positive and generally constant, substantially eliminates any cantilever effect, and permits the crystalor billet to be readily and easily extruded from the holder.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understoodthat variations and modifications can be effected within the spirit and scope of the invention.

1 claim:

1 In a device having a rotatably mounted, flat, annular member provided with a cutting portion extending along the central opening thereof for cutting into thin slices an element mounted within a holder having a guideway along which the element is movable in a first direction relative to the holder so as to position one end thereof relative to the central opening of the annular member to establish the thickness of the slice to be cut and movable with the holder in a second direction normal to the first direction, between a first position in which the one end is arranged within the central opening and a second position in which the one end is arranged in relation to the one surface of the annular member, a slice being cut from the one end by the cutting portion as the element is moved in the second direction from the first to the second position, the improvement which comprises:

first means fixed within and relative to the holder in a position generally opposite the guideway and having a portion for resiliently engaging the element adjacent the one end thereof; and

second means fixed relative to the other end of the element for movement therewith and having a portion for resiliently engaging the holder generally opposite the guideway;

the first and second means providing a generally positive and constant holding force at each end of the element throughout its full movement in both the first and second directions.

2. The device in accordance with claim 1 wherein the first means comprises an elongated resilient member having one end pivotally mounted in a fixed relation within the housing and a free end for engaging the element adjacent its one end and at a point generally opposite the guideway for maintaining the element in the guideway with a positive and constant force.

3'. The device in accordance with claim 2 including means arranged on the housing and engaging the free end of the elongated resilient member for changing the force with which the element is maintained in the guideway.

4. The device in accordance with claim 1 wherein the second means comprises a block member carried by the other end of the element and a biasing member fixed to and movable with the block member and resiliently engaging the housing for maintaining the element in the guideway with a positive and constant force.

5. The device in accordance with claim 4 wherein the biasing member comprises a pair of spaced, resilient arms, the arms straddling the first means as the other end of the element approaches the annular member, thereby maintaining the positive and constant force with which the element is maintained in the guideway throughout its full movement in both the first and second directions. 

1. In a device having a rotatably mounted, flat, annular member provided with a cutting portion extending along the central opening thereof for cutting into thin slices an element mounted within a holder having a guideway along which the element is movable in a first direction relative to the holder so as to position one end thereof relative to the central opening of the annular member to establish the thickness of the slice to be cut and movable with the holder in a second direction normal to the first direction, between a first position in which the one end is arranged within the central opening and a second position in which the one end is arranged in relation to the one surface of the annular member, a slice being cut from the one end by the cutting portion as the element is moved in the second direction from the first to the second position, the improvement which comprises: first means fixed within and relative to the holder in a position generally opposite the guideway and having a portion for resiliently engaging the element adjacent the one end thereof; and second means fixed relative to the other end of the element for movement therewith and having a portion for resiliently engaging the holder generally opposite the guideway; the first and second means providing a generally positive and constant holding force at each end of the element throughout its full movement in both the first and second directions.
 2. The device in accordance with claim 1 wherein the first means comprises an elongated resilient member having one end pivotally mounted in a fixed relation within the housing and a free end for engaging the element adjacent its one end and at a point generally opposite the guideway for maintaining the element in the guideway with a positive and constant force.
 3. The device in accordance with claim 2 including means arranged on the housing and engaging the free end of the elongated resilient member for changing the force with which the element is maintained in the guideway.
 4. The device in accordance with claim 1 wherein the second means comprises a block member carried by the other end of the element and a biasing member fixed to and movable with the block member and resiliently engaging the housing for maintaining the element in the guideway with a positive and constant force.
 5. The device in accordance with claim 4 wherein the biasing member comprises a pair of spaced, resilient arms, the arms straddling the first means as the other end of the element approaches the annular member, thereby maintaining thE positive and constant force with which the element is maintained in the guideway throughout its full movement in both the first and second directions. 